feat(dashboard): a curated default layout, merged duplicate widgets, a labelled Overview (#5213)

- New installs start from widgets.RECOMMENDED, packed row by row for the
  enabled plugins; the edit drawer can reset a dashboard to it.
- Host Agent — Resources folds into Hosts — Overview (which gains load 1m),
  UniFi — Devices into UniFi — Overview; migration 0032 moves existing
  dashboards onto the survivors.
- The Overview labels what it counts (hosts, monitors up/down/pending,
  alerts firing) and lists firing alerts and down monitors with since-times.
- Uptime polls every 5 minutes (poll_seconds) instead of every cycle.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/templates/hosts/overview_widget.html

@@ -34,6 +34,7 @@
       {% if a.get('cpu_pct') is not none %}<span title="CPU — value + last-hour trend" style="display:inline-flex;align-items:center;gap:0.3rem;{{ threshold_style(a.cpu_pct, 'cpu') }}"><span style="color:var(--text-dim);">cpu</span> {{ "%.0f"|format(a.cpu_pct) }}%{% if spark %}<span style="line-height:0;opacity:0.85;">{{ spark | safe }}</span>{% endif %}</span>{% endif %}
       {% if a.get('mem_used_pct') is not none %}<span title="Memory" style="{{ threshold_style(a.mem_used_pct, 'mem') }}"><span style="color:var(--text-dim);">mem</span> {{ "%.0f"|format(a.mem_used_pct) }}%</span>{% endif %}
       {% if a.get('disk_root') is not none %}<span title="Root filesystem (/)" style="{{ threshold_style(a.disk_root, 'disk') }}"><span style="color:var(--text-dim);">disk /</span> {{ "%.0f"|format(a.disk_root) }}%</span>{% endif %}
+      {% if a.get('load_1m') is not none %}<span title="Load average over 1 minute: processes running or waiting to run"><span style="color:var(--text-dim);">load</span> {{ "%.2f"|format(a.load_1m) }}</span>{% endif %}
       {% if not a.fresh %}<span title="Agent data is stale" style="color:var(--yellow);">stale</span>{% endif %}
       {% else %}
       <span style="color:var(--text-dim);" title="No agent reporting">no agent</span>